Cold-worked pipe and method of obtaining the same



April H, 1950 L. F. SATTELE ETAL. I 2,503,512

COLD-WORKED PIPE AND METHOD OF OBTAINING THE SAME Filed Aug. 2, 1946 FIEJL mwm m; 100/5 F 5477545 m/ fP/TZ jaw/a r Patented Apr. 11, 1950 COLD-WORKED PIPE AND METHOD OF OBTAINING THE SAME Louis F. Sattele and Fritz M. Scharff, Lorain, Ohio, assignors to National Tube Company, a. corporation of New Jersey Application August 2, 1946, Serial No. 687,992

2 Claims. 1 This invention relates to cold-worked pipe having enhanced physical properties and balanced yield strengths and to the method of cold working the same whereby the desired improved physical properties are obtained.

The use of relatively large diameter pipe for gas lines and other uses wherein the pipe is subjected to internal pressures has resulted in increasingly thinner walls or so-called higher D/t ratios. This has come about for various reasons, such as, ease in handling the large pipe sections, and lower shipping costs, in addition to the initial cost of the pipe. Consequently, the search for methods or ways of obtaining suitable physical properties economically has been intensified. While these can be obtained by the use of suitable alloying ingredients, the cost thereof in many instances is so high as to render such additions uneconomical. Also the use thereof or resort to higher carbon and manganese contents results in welding difiiculties or problems that render the same undesirable. Cold-working has heretofore been proposed as a means of increasing the physical properties. However, the frequently practiced cold-rolling wherein the diameter is reduced, has little beneficial effect on properties resulting in higher resistance to internal pressures. Conversely the cold expansion of the pipe by forcin the same over a ball or by hydraulic pressure has resulted in a large increase in the yield point in tension in a circumferential direction but has much less effect on the yield point in tension in a longitudinal direction. Consequently, such treatment has resulted in unbalanced transverse and longitudinal yield strengths which is undesirable and uneconomical since the resistance to internal pressure depends on both.

Accordingly, it is an object of the present invention to provide an improved method of coldworking pipe.

It is another object to provide a method of cold-working pipe to obtain enhanced physical properties and balanced yield strengths.

It is a further object to provide pipe having enhanced physical properties and balanced yield strengths.

It is still another object to provide a method of obtaining enhanced physical properties and balanced yield strengths in an economical and expeditious manner.

The foregoing and further objects will become apparent from the following specification when read in conjunction with the attached drawing, wherein:

Figure 1 is a plan view, partly in section;

Figure 2 is a side elevation; and

Figure 3 is a section on lines III-III of Figure 2.

Seamless pipe composed of medium carbon steel containing between .15 and .50 9?- carbon and .30 to 2.00% manganese and produced by conventional hot rolling methods has a longitudinal yield point in tension which generally is slightly higher than the yield point in tension in a transverse direction. For example, longitudinal and transverse test pieces were taken from representative pieces of a number of lengths of hot rolled seamless pipe containing between .17 and 27% carbon and .44 to .79% manganese. The longitudinal specimens when tested in tension showed a .5% strain yield strength of 48,271 p. s. i., whereas the transverse specimens when tested in tension showed a .5% strain yield strength of 47,500 p. s. i.

If pipe is expanded while at cold-working tem peratures, the yield strength in a transverse direction will be increased considerably more than the longitudinal yield strength. For example, sections from the foregoing lengths of pipe were cold expanded 2.4 to 2.8% by forcing a ball mandrel therethrough. The average .5% strain yield strength of longitudinal specimens taken therefrom was 55,300 p. s. i., and the .5% strain yield strength of transverse specimens was 65,000 p. s. i. From this, it is seen that the longitudinal yield strength was increased 7,030 p. s. i. or about 15%, whereas the transverse yield strength was increased 17,500 p. s. i. or about 37% i. e., over twice as much as the longitudinal yield strength. Such a condition of course causes an unbalanced condition in the pipe and moreover the increase in transverse yield is largely wasted because the longitudinal yield has not been similarly increased.

We have discovered if the pipe is subjected to alternate tensile and compressive stresses alternately applied progressively along the length of the pipe at the point where the pipe is being slightly expanded while at cold-working temperatures that the longitudinal yield strength can be increased in much greater proportion to the transverse than the foregoing and the two will be in substantial balance. Thus, sections of the same lengths of pipe from which the foregoing specimens were taken were expanded and simultaneously with the expansion, and at the point of expansion, the pipe was progressively flexed around the periphery thereof to provide alternate tensile and compressive stresses therein.

3 Longitudinal specimens from the sections so treated had an average .5% strain yield strength or 65,350 and the average yield strength of the transverse specimens was 67,880 p. s. 1. Hence, it is seen that the longitudinal yield has been increased 17,279 p. s. i. or about 36% and transverse yields have been similarly enhanced about 20,380 p. s. i. or about 43% and that they are in substantial balance. In any event, such increase should amount to at least 30% and the two yield strengths should be within 6% of absolute balance. For uniform results, the expansion should involve a diameter increase of the order of at least 2%.

Referring to the accompanying drawing, there is shown diagrammatically suitable apparatus for carrying out the invention. The numerals 2 and 4 designate metal working rolls providing a converging or feeding zone A and a slightly diverging and expanding zone B. Intermediately disposed between the rolls is. a mandrel plug 6 having a slightly tapered zone C. The metal working rolls have their axes of rotation crossed so that the workpiece W is rotated and simultaneously advanced thereby with a helical motion. As the workpiece is engaged by the feeding zone A, it is distorted into an oval shape whereby, due to its'rotation, longitudinal and compressive stresses are alternately applied around the periphery and progressively along the length thereof. In this operation, the wall thickness is not reduced materially beyond the reduction inherent in the expansion.

While we have shown and described one specific embodiment of our invention, it will be understood that this embodiment is merely for the purpose of illustration and description and that various other forms may be devised within the of said tube containing between .15 and .50%-

carbon and having a yield point in tension in a longitudinal direction and a yield point in tension in a circumferential direction which are within 6% of absolute balance, said balance being obtained by applying alternate tensile and compressive stresses concurrently with an expansion of the diameter of the tube while at cold-working temperatures.

LOUIS F. SATTELE.

FRITZ M. SCHARFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,288,344 Wills Dec. 17, 1918 1,951,348 Diescher Mar. 20, 1934 1,957,427 Buchholtz May 8, 1934 2,176,155 Stiefel Oct. 17, 1939 2,188,138 Malcolm Jan. 23, 1940 2,309,690 Aiken Feb. 2, 1943 

